python: don't use libressl for host build

python: don't use libressl for host build

Fixes: https://github.com/openwrt/packages/issues/3767
Since commit:
https://github.com/lede-project/source/commit/f6e6341d896adb78f9b496f71aab8f45e1742d5a

libressl is built on the host-side.

Python picks it up [ via the openssl/* headers ] and assumes
it has SSL libs.
Compiling works fine, linking fails.
Doesn't look like it's because:
https://github.com/lede-project/source/commit/2fd5ce9488d11c7e6eee7dc30f128bd12be889f5

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>